1. Field of the Invention
This invention relates to immunoassay methods for detecting the presence of antibodies to viral antigens in test samples derived from human blood. The detection of viral antibodies in a patient's blood is indicative of past or current viral infection. Such information can be of great clinical value, particularly in prenatal screens to determine risks from infections due to such viral agents as cytomegalovirus, Rubella virus, herpesvirus, and the like or to determine success obtained with vaccinations against viral diseases such as measles, Rubella, mumps, polio and the like.
It is evident that a most desirable feature of any clinical assay is the ability to perform the assay on an easily obtainable sample with a minimum of sample pretreatment. Where the object of an assay is a component of blood, obviously the most desirable assay sample would be whole (or untreated) blood. However, as demonstrated below, the previously known immunoassays for viral antibodies have consistently been limited to assaying treated blood samples, primarily serum. Procedures for obtaining serum samples from whole blood samples require the use of apparatus and the skills of a technician, both of which add to assay time and cost. It has been discovered that, contrary to the prejudices raised by the prior art, the present immunoassay method can be used to assay whole human blood samples.
2. Brief Description of the Prior Art
Over the years, several different techniques have evolved for the determination of viral antibodies including complement fixation, hemagglutination, and, more recently, various immunoassays such as radioimmunoassay and enzyme immunoassay. Under the current state of the art, the method of choice is an immunoassay technique referred to as the indirect, solid-phase immunoassay.
In such a method for detecting an antibody to a viral antigen (hereinafter such antibody being abbreviated as "Ab.sub.1 " and such antigen as "Ag"), a test sample, such as serum, derived from human blood is incubated with a solid-phase (i.e., immobilized or insolubilized) form of Ag whereby any Ab.sub.1 present in the test sample becomes bound to the solid-phase Ag. After this first incubation, the resulting solid-phase Ag-Ab.sub.1 complexes are separated from the test sample and a label-incorporated form of an antibody to Ab.sub.1 (such labeled antibody being abbreviated as "Ab.sub.2 *") is contacted with the separated, solid-phase Ag-Ab.sub.1 complexes. Where the label is radioactive, the assay is known as a radioimmunoassay. Other, nonradioisotopic, techniques can also be used. Where the label is an enzyme, the assay is known as an enzyme immunoassay.
After a second incubation period, the resulting solid-phase Ag-Ab.sub.1 -Ab.sub.2 * complexes are separated from excess Ab.sub.2 *. Then, the amount of the label in the separated, solid-phase Ag-Ab.sub.1 -Ab.sub.2 * complexes is measured and is a function of the presence or amount of Ab.sub.1 in the test sample. If a significant amount of Ab.sub.1 is present in the sample, it will become bound to solid-phase Ag and thereafter by Ab.sub.2 * so that the association of the label with the solid-phase in significant amounts is due to the presence of Ab.sub.1.
This indirect, solid-phase immunoassay technique can be schematically illustrated as follows: ##EQU1##
Representative of the known indirect, solid-phase immunoassays for viral antibodies are the procedures described in the following references: for the detection of antibodies to cytomegalovirus--Archives of Virology 58: 253 (1978), J. Immunol. 117: 2006 (1976), Brit. J. Exp. Pathol. 57: 243 (1976), and J. Infect. Dis. 136 Suppl. 5337 (1977) and for the detection of antibodies to Rubella--Brit. J. Exp. Pathol. 56: 338 (1975), J. Clin. Microbiol. 4: 117 (1976), Infection and Immunity 19: 369 (1978), Acta Path. and Microbiol. Scan. Section B 85: 113 (1977), Clin. and Exp. Immunol. 31: 50 (1978), and Res. Comm. Chem. Pathol. and Pharm. 19: 281 (1978). All of the above described techniques are directed specifically and solely to the assay of serum. Such references further reinforce the prejudice against performing the involved immunoassays on whole, untreated blood samples, a course of action which would clearly be more advantageous in terms of cost, convenience, simplicity and assay time.